What I have learned from matching the 6x4 tube varieties with 12AU7s and 12AT7s that you can obtain most any sonic flavor you seek. For example, I have found matching a 50s black plate 12AU7 RCA with Raytheons mentioned above will provide a warm, smooth, and creamy sound. I would be interested in your favorite combos. Since I have not had much previous experience with 6V6 tubes, so I will spend sometime with this tube before moving on to 5881 or 6Ls.

hi, I just bought a pair of blackplate philips 6x4 and am listening to the combo with a pair of 12at7 from Mullard, Nos. The problem however is that the 6x4 do not fit tightly into their sockets, which makes them lean to one side and generally vulnerable to shocks (what if teh ceiling falls on my Mini Torii ... Is there a solution to that? I am not familiar with pin bending and am a li'l reluctant to try.

I bought another pair of 6x4 nos sylvania rectifiers and surprise, they also whistle, just like the premium nos philips I tried a few months back. I do not understand and I do not want to keep buying 6x4's randomly!!!! I doubt that the amp has a problem, or the tubes themselves, but something eludes me, can you please help? They strat whistling a few hours after power up, but I have not carried out extensive research ( I just had a research methodology exam yesterday, in clinical psychology )Thank you very much. If you are at all interested I would gladly exchange with you or simply buy from you any nos 6x4 that is tested and working in your mini torii, Or perhaps you could suggest a brand and I can find it somewhere!!!!!Thank youRaduschka

I suppose it is not related to the other tubes I am using, which are all up to specs.On the other hand, other 6x4 I have work just fine... Are there several types of 6x4? I remember reading somewhere about the wa type, rated for a different altitude?! I noticed that the new mini torii model comes with a different type of rectifier alltogether. My right channel has developed a hiss that goes away after half an hour or so, I may have to send it home (to Steve that is) for a fix soon.Anyway, thank you very much

Just understand that the 6X4 is the weak link in the amp. If you have power tubes that bias way too high it could take one of the 6X4 down. A clue that this is happening would be if the 6X4 glows too bright. If you have some 6X4WA you could probably use them with a 6V6, 6K6, 6L6 but not with a 6Y6. I have never tried a 6F6 myself.

I am only using 6v6, but prefer oc3 to oa3 and the other 2 varieties. Could it be that this combination puts a stronger load on the 6x4? The 6x4 don't glow particularly bright.I am back to the Jan Philips wa now, but enjoyed the Sylvania much more.... Is there any brand that you would recommend?

It is my understanding that the 6x4, especially the WA version, was the weak link in the amp. Also they are no longer being produced. The 9 pin EZ81/6CA4 is in current production. This is another factor. I think they sound roughly equivalent to one another. The EZ81 is not going to fail if a power tube is biased very high.